The present invention is directed toward circuit boards or substrates for devices such as printed circuit boards. In order to adapt these circuit boards as substrates for electronic devices which may be present in very large numbers, it is commonly necessary to provide often complex circuitry on both external and internal surfaces of the boards in order to achieve signal transmission necessary for proper operation of the devices.
The term "circuit board" is employed herein to include printed circuit boards and other device substrates such as integrated devices, multi-chip modules and similar devices having signal traces on different layers.
Substantial effort has been expended in the prior art in order to improve signal transmission capabilities in such circuit boards. For example, printed circuit boards are commonly provided with large numbers of signal transmitting circuits on at least one signal layer of the boards. More commonly, such circuits are formed on multiple layers of the boards including both external surfaces of the boards as well as one or more internal surfaces. Even with such arrangements, space is critically limited on such boards for achieving various functions contemplated in connection with devices to be mounted on the surfaces of the boards. Accordingly, the prior art has been concerned with designs and configurations for such circuit boards permitting the use of even larger numbers of circuits for signal transmission between various portions of the circuit boards.
For example, U.S. Pat. No. 4,891,789 issued Jan. 2, 1990 to Quattrini, et al. disclosed a surface mounted multilayer memory printed circuit board designed and constructed with its top and bottom layers containing repetitive integrated circuit (IC) chip component hole/pad and interconnection line patterns preferably forming mirror images of one another. The board of this patent used surface mounted techniques in which the integrated chip components of the memory array were mounted and soldered to both sides of the board thereby doubling the density or capacity of the memory board. The integrated circuit memory chips, mounted on the top and bottom surfaces of the board, were aligned with each other for sharing common through-holes or vias in which logically equivalent input connections were exchanged in a manner for reducing the number of holes and links of connective wiring.
The above reference demonstrates the need for substantial signal transmitting circuits on printed circuit boards as well as other components mounted for example on the surfaces of the printed circuit board to provide a substrate for various electronic devices.
The above patent is also illustrative of the use of through-holes or vias which are characterized as elements formed from conductive material and extending partially or entirely through the circuit board in the Z direction for transmitting signals between various layers of the board. Through-holes and vias are both well known devices for achieving such signal transmission.
As noted above, other types of circuit boards or device substrates similarly employ large numbers of circuits for signal transmission between various portions of the circuit boards and/or devices mounted thereon. For example, U.S. Pat. No. 4,739,448 issued Apr. 19, 1988 to Rowe, et al. disclosed a microwave multiport multilayered integrated circuit chip carrier including multiple signal layers. U.S. Pat. No. 4,959,708 issued Sep. 25, 1990 to Henderson, et al. disclosed an MOS integrated circuit in which a plurality of MOS devices are arranged or mounted upon a substrate and interconnected with each other and with signal, power and ground pads in multiple electrical circuits adapted to process separate electrical signals.
U.S. Pat. No. 4,613,771 issued Sep. 23, 1986 to Gal disclosed a similar integrated circuit wherein a circuit was integrated into a substrate with improved noise immunity being provided by various components.
Many prior art references such as the representative ones noted above illustrate the need for large numbers of signal transmitting circuits in such substrates. The representative references discussed above also commonly employ conductive elements extending in a Z direction through the substrate for providing signal communication between different levels of the circuit boards. These conductive elements are generally similar to the through-holes and vias discussed initially above.
Yet another prior art approach for providing large numbers of circuits subject to "customization" employed interconnects as building blocks for electronic circuitry and microcircuitry to typically receive and support further electrical devices or substrates capable of being electrically interconnected with each other to provide larger, more complex electrical structures. So-called "programmable interconnects" were then employed in order to permit mass production of substrates with their circuitry subsequently being programmed to produce a variety of wiring plans as required by a user.
Such an arrangement was disclosed for example in U.S. Pat. No. 4,458,297 and in Australian Convention application No. 610,249 by Microelectronics and Computer Technology Corporation.
These references disclosed yet another approach for providing complex and yet programmable circuitry in circuit boards of the type contemplated by the present invention. More specifically, the circuit boards contemplated by these references may be adapted for a variety of applications or uses. However, they are also representative of circuit boards or substrates wherein it is desirable to transmit signals throughout one or more X-Y planes of the substrate as well as possibly in a Z direction through the substrate.